1. Field of the Invention
This invention relates to semiconductor inspection and, more particularly, to inspection systems and methods for transferring and processing inspection images.
2. Description of the Related Art
The following descriptions and examples are given as background only.
Semiconductor devices, such as logic, memory and other integrated circuit devices, are fabricated by processing a specimen (such as a semiconductor wafer) to form various features and multiple levels of the semiconductor device. Lithography is one example of a semiconductor fabrication process that may be used to transfer a pattern to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices can be fabricated in an arrangement on a semiconductor wafer and then separated into individual semiconductor devices.
Inspection methods are used at various stages of the manufacturing process to detect defects on the wafers. Inspection has always played an important role in semiconductor fabrication. However, inspection has become increasingly important to the successful manufacture of acceptable semiconductor devices as the dimensions of the devices continue to decrease. For instance, detecting defects of decreasing size has become increasingly necessary, since even relatively small defects may cause unwanted aberrations in the semiconductor device, sometimes causing the device to fail.
Many different types of inspection tools have been developed for the inspection of semiconductor wafers, including optical and E-beam systems. Most optical inspection tools can be characterized into bright-field (BF) and dark-field (DF) systems. Bright-field systems direct light to a wafer at a particular angle and measure the amount of light reflected from the surface of the wafer at a similar angle. Bright-field systems typically use high-resolution imaging optics, and the inspection of the wafer is performed in such a manner that the pixel size is very small. The small pixel size takes advantage of the high-resolution imaging optics and the large amount of reflected light to generate inspection images with a great amount of detail. As such, BF systems are typically used for imaging patterns (e.g., memory cells or circuit features) formed on the wafer.
On the other hand, dark-field systems detect the amount of light, which is scattered from the surface of a wafer when an incident beam is supplied to the wafer at a normal or oblique angle. In the case of dark-field inspection, smooth surfaces lead to almost no collection signal, while surfaces with protruding features (such as patterned features or defects) tend to scatter much more strongly (sometimes up to six orders of magnitude or more). As such, DF systems are typically used for detecting defects or particles that may be present on a patterned or unpatterned wafer. Darkfield illumination provides a larger pixel-to-defect ratio than bright-field illumination, permitting faster inspections for a given defect size and pixel rate. Darkfield imaging also permits Fourier filtering to enhance signal to noise ratios. Some inspection tools reap the benefits of both systems by combining bright-field and dark-field techniques within the same tool.
Regardless of the type of inspection system used, the inspection images must be analyzed to determine whether a wafer is acceptable. In some inspection systems, one or more sensor arrays may be used to detect light propagating from the wafer in response to BF or DF illumination light. Charge coupled device (CCD) and time delay integration (TDI) cameras are two examples of sensor arrays commonly used for this purpose. As illumination light is scanned across the surface of the wafer, the sensor arrays convert the detected light into electrical signals, which are typically transferred in parallel, via multiple data channels, to one or more processing nodes of the inspection system. The processing nodes may utilize a variety of different algorithms to analyze the electrical signals (i.e., the image data) for defect detection.
The image data obtained by the sensor array is usually analyzed by a number of processors connected together in series, or in parallel. In the serial configuration, the parallel image data from the sensor array is supplied to a first processor. After serialization, the first processor performs one step of the analysis and the resultant data is supplied to the next processor in the serial chain for the next step in the analysis algorithm. The image data may be fed into any number of serially-coupled processors, with each processor in the chain performing some small portion of the total analysis algorithm. In the parallel configuration, inspection speed is improved by supplying the parallel image data to all processors at the same time. Each processor may be coupled for receiving the entire inspection image, or only a portion of the image data. As such, the parallel processors may perform separate analysis algorithms, or different steps of the same analysis program.
Regardless of the processing configuration used, conventional inspection systems typically fail to maximize inspection speed, reliability and scalability. As noted above, most inspection systems transfer image data to the processing nodes in parallel. Such data transfer methods suffer from limited data transfer rates, signal integrity problems and require numerous wires and connectors, which are bulky and unreliable. In addition, many inspection systems locate processing nodes inside the inspection tool, itself. As set forth below, internal processing nodes are often limited in space, power, processing capabilities and scalability.
FIG. 7 illustrates one embodiment of a conventional inspection tool 600 including illumination subsystem 610 for providing illumination light to specimen 620, collection subsystem 630 for collecting light propagating from the specimen and detection subsystem 640 for detecting light collected by the collection subsystem. The image data from detection subsystem 640 is transferred in parallel, via multiple channels (e.g., channels CHO-CHN), to a processing subsystem within the inspection tool. In one embodiment, the processing subsystem may include analog-to-digital converter (ADC) 650 for digitizing the image data and interface card 660 for serializing the image data. A number of parallel buses (e.g., buses B0-BN) are used to couple the ADC to the interface card. The buses typically use a relatively high speed bus protocol, such as low voltage differential signaling (LVDS) or HyperTransport, to transfer the parallel image data between the ADC and interface card.
As shown in FIG. 7, digital signal processor (DSP) boards 670 are included within inspection tool 600 for processing the image data to detect defects. The DSP boards may include any number of processors coupled together on a common backplane. The individual processors may be coupled in series or in parallel, as discussed above. The inspection results from the DSP boards may be supplied, via a PCI bus, to host computer 680 for analysis and display. In some cases, the host computer may supply control signals (such as clock, synchronization and encoder signals) to the ADC and backplane components via a cable (690) connecting the host computer to the inspection tool.
The inspection tool shown in FIG. 7 presents various problems. First of all, the inspection tool fails to maximize data transfer speed, signal integrity and reliability by transferring the image data in parallel. Second, data processing is conducted by DSP boards located within the inspection tool. These boards are limited in space, power and processing capabilities. In most cases, the DSP boards lack scalability, and therefore, cannot be expanded to incorporate new features as they are developed.
A need exists for a wafer inspection system that overcomes the disadvantages mentioned above. In particular, a need exists for an improved wafer inspection system that performs a majority of the image data processing outside of the inspection tool. In addition, a need exists for an improved wafer inspection system that uses high speed serial data transfer methods to transfer image data outside of the tool.